1. Field of the Invention
The present invention relates to a new thermoplastic polyester resin, a process for producing the same, and an orthopedic cast material produced therefrom. More particularly, this invention relates to a new thermoplastic polyester resin having a low melting point which is useful as a molding material, especially as an orthopedic cast material, a process for producing the same, and an orthopedic cast material produced therefrom.
2. Description of the Prior Art
Heretofore, calcined gypsum has been in general use as the orthopedic cast material to immobilize the broken limb and joint. However, this cast material is undesirable for patients because it is heavy, bulky, and soluble in water. In order to overcome these disadvantages, there has been developed an orthopedic cast material made of thermoplastic resin impregnated into a backing web such as a gauze and reticulate knitted or woven fabric, and polycaprolactone of high molecular weight has been proposed as such a thermoplastic resin (U.S. Pat. No. 3,692,023). This polymer, however, has a disadvantage that it has to be made soft, prior to application to a patient, by heating to a temperature above 60.degree. C. which is the melting point of this polymer. This heat causes pain to the doctor and patient. To alleviate pain, it is considered to lower the melting point, and the heating temperature accordingly, by adding a plasticizer to the polymer. However, the plasticizer will cause another problem. That is, it harms the skin and lowers the mechanical strength of the resulting cast material. This is particularly true when an ester-type plasticizer is used. Under these circumstances, there has been a demand for a plastic cast material that can be applied at a temperature below 60.degree. C.
The present inventors carried out a series of researches on this subject. As the result, it was found that a new thermoplastic polyester resin prepared by copolymerizing a specific aliphatic dicarboxylic acid, a specific aliphatic diol, and polycaprolactone of high molecular weight has a melting point lower than 60.degree. C. and has strength high enough for use as cast material. The present invention is based on this finding.